SEWAGE AND MUNICIPAL WATER IN AN URBAN CREEK IN THE NORTHEAST: A TALE OF AGING INFRASTRUCTURE

Aging infrastructure and an increase in extreme precipitation are challenging sanitary and stormwater systems in the Northeast, and water quality is suffering as a result. The Hans Groot Kill (HGK) is a small urban stream in Schenectady NY that has been integrated into the stormwater collection system. We used fecal indicator bacteria (FIB, here Enterococcus) to show impairment of the entire creek. Pathogen data show the HGK is severely contaminated: in the last two years every sample exceeded the EPA beach advisory value. Repeated sampling showed that several outfalls have particularly high pathogen levels. In 2022 the City used genetic marker HF182 to show that the contamination is definitively tied to human sewage. The suspicion is that untreated sewage enters the HGK from impaired sanitary sewer lines, and therefore a primary driver of FIB may be exfiltration from these lines. There is a clear relationship between rainfall and high FIB, but there are also samples with high FIB in low-flow conditions, meaning that some sewage leaks are chronic. While raw sewage is a primary concern, little attention has been paid to the possibility that drinking water pipes may also be leaking. This matters because leaking sanitary sewer and drinking water pipes can allow sewage and pathogens to mix due to pressure loss, which is relevant given past enteric disease outbreaks following water main breaks. Fluoridated municipal water can be used as a tracer because municipal concentrations are ~10x the geogenic levels in this area. The City of Schenectady uses fluoridation with a target level of 0.7 mg/l. Using fluoride as a tracer shows that about 1/3 of the water in the HGK at low-flow conditions is from the City water supply. Fluoride concentrations are higher at low flow, hence municipal water makes up a greater fraction of the water (typically 20-40%, with single sources between 50-65% municipal water). At this point we cannot determine the fractional contribution of drinking water vs. waste water. Clearly there is a significant sewage load in this stream, as indicated by high and persistent FIB levels that make this water unsafe for contact. In the last two years, continued FIB testing by our group at Union College, the NYSDEC, and an environmental consulting firm has demonstrated that the contamination persists despite mitigation attempts.